help me learn

[dre22]

I looked at lots of forms and books. I even learned how to read schematics and even build circuits. But I still cannot fix broken circuit boards or trouble shoot them, someone please tell me how i can learn. If it be by web site book or even you. Please help me i really want to learn how.
Thank you very much for your
help,,,

dre22

 

[Nigel Goodwin]

I looked at lots of forms and books. I even learned how to read schematics and even build circuits. But I still cannot fix broken circuit boards or trouble shoot them, someone please tell me how i can learn. If it be by web site book or even you. Please help me i really want to learn how.

It's not something you can learn from a forum post, essentially it's mostly down to experience - but also down to understanding how a circuit works, so you need a good knowledge of electronics. Once you know how something works you know where to look to see why it's not working.

 

[ThermalRunaway]

Learning to fault find is a barrier you're best of pushing through on your own by gaining your own experience. You can act on advice by others, but the fault finding work itself has to be your own. It takes years to gain a good fault finding skill and it's all about experience, electronics knowledge, and commitment to keep going even on the really tough faults!

Unfortunately, the Electronics Diagnosis trade is in such a state these days that companies no longer feel that they need to pay for a fault finding skill. Even though the skill takes years and years to learn, and is subject to an in depth Electronics background, they still don't feel the need to pay for it and in some cases, they don't need to anymore!

Brian

 

[akg]

this thread might be interesting .

https://www.electro-tech-online.com/threads/how-do-you-people-do-it.23012/?highlight=guys

 

[ClydeCrashKop]

Manufacturers don’t want you to fix them. Sometimes they use fictitious part numbers on ICs so you can’t identify them. Unless you have inside information, the best you can do is look for burnt traces and components and replace them but it may be another component or a loose piece of solder bouncing around that caused the problem.

 

[Sudonon]

I agree with ClydeCrashKop. Try fixing the obvious but if it's fried you need to find the cause.
The first thing I do is to insure that I have data for all the components.
Then I decode the board. You need to follow every trace and draw out the schematic. If you don't have data or are unable to understand the shematic you are lost.
Once I have the schematic I test components - check resistors ,capacitors etc. If you want to check a transistor you usually need to isolate it or desolder it. The easiest way to check IC's is by replacement but that can be expensive.
Do not apply power if you do not understand the danger. If it's high voltage or high current you could kill burn or blind yourself.
Then I apply power using a current limited bench supply or small batterys and start checking the power circuit traces and the voltage at each IC and transistor and the temperature (if it's to hot to touch it's likely a problem).
If the board has multiple supply voltages I try to start with the lowest.
Be prepared to spend a lot of time.
Good luck
ps: This is the first time I have tried using color for emphasis - hope it works

 

[Nigel Goodwin]

I agree with ClydeCrashKop. Try fixing the obvious but if it's fried you need to find the cause.
The first thing I do is to insure that I have data for all the components.
Then I decode the board. You need to follow every trace and draw out the schematic. If you don't have data or are unable to understand the shematic you are lost.
Once I have the schematic I test components - check resistors ,capacitors etc. If you want to check a transistor you usually need to isolate it or desolder it. The easiest way to check IC's is by replacement but that can be expensive.

This is a VERY slow,expensive, and cumbersome repair method!.

As I said previously, you need to understand how the circuit works, then from the symptoms you 'should' know where to start looking. Depending what it is, and what the fault is, you can then start taking voltage measurements, checking signals with a scope, or injecting test signals (or all three!).

A common technique is the 'half split' method - imagine you have a unit with 12 distinct stages, if you check at the midpoint (again either injecting a signal, or testing for one) you can easily eliminate half of the circuit. Next half it again, this time your possible fault location is down to only three stages. Do the same again and again, until you have the fault located in one specific stage, then do more detailed fault finding on that stage, you may even be able to 'half split' within the faulty stage.

 

[dknguyen]

Just build lots of circuits. I guarantee you that something will go wrong and you will have to debug it. Since you know how the circuit should work (you did design it or understand it before you built it right?) then you can logically see what's wrong and hunt through different things that might cause that problem.

 

[HiTech]

I agree with Nigel: understanding the circuit through its stages, isolating the problem stage, and then zeroing in on key components that are the likely culprits. Following foil traces and drawing schematics is just crazy IMHO! That technique might help after you've isolated the defective stage... and even then it's faster to mentally visualize or map out the stage's schematic in your mind... if you are of avg. intelligence and aptitude.

 

[Nigel Goodwin]

Following foil traces and drawing schematics is just crazy IMHO!

If you don't have a circuit diagram, drawing it out is a very valuable technique, I've drawn many out over the years where diagrams aren't available. It's also a good learning experience, it's surprisingly educational - if a bit of a pain in the rear!.

But bear in mind, drawing the circuit out isn't a fault finding technique in itself, it's simply to give you a circuit to allow you to fault find.

BTW, most I've drawn out over the years have been audio amplifiers, in fact I've drawn out two old PA amplifiers in the last couple of years. For repair reasons you don't normally have to draw the entire circuit, just the section with the fault - usually the power amplifier!.

 

[HiTech]

I mentioned that coming from the idea of using that as a primary troubleshooting method which then is a time waster for the most part and not practical if you are on the clock making money for yourself and a company. I have drawn diagrams when necessary, but prolly a meager 5% or less of all the equipment I have repaired over the years. I've always been able to mentally sketch the circuit (of that stage) in my head as I look over the board.

 

[Nigel Goodwin]

I have drawn diagrams when necessary, but prolly a meager 5% or less of all the equipment I have repaired over the years.

I've drawn out FAR, FAR less than that over the years - probably only one every five or ten years?.

The PA amps the other year were a bit of an exception, I was given two old amps, and I wanted to modify them both - so required a circuit, both were obscure makes, so they weren't available.

 

[HiTech]

I've drawn out FAR, FAR less than that over the years - probably only one every five or ten years?

Do you keep pencils and pens around the house?